Prior attempts to achieve acceptable flame-resistant polyester/cotton or nylon/cotton blends have not met with commercial success. None of the treatments is practical from the consumer point of view, producing fabrics that have a very stiff hand. This is because in order to achieve the requisite flame-resistant properties, a high chemical add-on is required. This add-on makes the fabric stiff, masks the color of the underlying fabric, and often imparts an acrid or unacceptable odor to the fabric. In addition, the performance of the flame-resistant fabrics is often unreliable.
Most of the previous work conducted on flame-resistant polyester/cotton or nylon/cotton blends used a single chemical system that was targeted for the cotton component of the blend. The approach was to "load" the fabrics with a flame retardant specific for cotton, for instance THPS [tetrakis-(hydroxymethyl)phosphonium sulfate]. It was not unusual with these earlier products to use from 30 to 35% of fixed chemical add-on in order for the polyester/cotton or nylon/cotton blend fabric to pass a bottom vertical flame test. Regrettably, however, the aesthetics of the finished fabrics were poor, as they have a very stiff hand and the appearance of a coated fabric. The add-ons used for these products were far in excess of the theoretically required amounts.
When THPS is applied to a polyester/cotton or nylon/cotton blend, flame resistance results. Since the THPS is specific to cotton, it does not react with the polyester or nylon content of the fabric but simply physically coats the synthetic component. As a result, after multiple launderings, that portion of the flame retardant surrounding the polyester or nylon fiber is partially lost. In consequence, it was not unusual to use as much as 5.5% phosphorus add-on for a polyester/cotton blend, at least initially, in order to result in the target 3% of fixed phosphorus after 50 launderings in hot water.
In the 1970's, polyester/cotton blends were flame retarded using tris-2,3-dibromopropyl phosphate ("Tris") in combination with THPS. However, "Tris" was found to be a carcinogen and was withdrawn from the market, so that there is no predominantly-polyester blend of polyester and cottom sold today that has been treated with flame-retardant chemicals. An object of the present invention is to produce acceptable flame-resistant polyester/cotton and nylon/cotton blends using multiple flame-retardant chemicals or chemical systems, and to employ processing conditions or adjuvants that produce a commercially acceptable, attractive product having good color and acceptable hand.